Stent delivery system using shape memory retraction

ABSTRACT

The inventive stent delivery system includes a catheter having a retractable outer sheath near its distal end. A shape memory contraction member having a memorized contracted shape is connected to the retractable outer sheath. A heat generating device connected to the shape memory contraction member causes the shape memory contraction member to heat up to its transition temperature and assume its contracted position, retracting the retractable outer sheath. Another embodiment utilizes 2 springs, a “normal” spring and a shape memory alloy (SMA) spring, the two springs selected and designed so that the “normal” has an expansion force which is less than SMA spring when the SMA spring is austenitic, but greater than the SMA spring when the SMA spring is martensitic. Yet another embodiment utilizes a shape memory latch which in its martensitic state abuts a stop to prevent a spring from moving the sheath proximally, but in its austenitic state releases the stop, allowing the spring to retract the sheath to release the stent for deployment.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional application from applicationSer. No. 09/283,444, which is a continuation-in-part of U.S. applicationSer. No. 09/204,644, filed Dec. 2, 1998, which is a continuation of U.S.application Ser. No. 08/947,619, filed Oct. 9, 1997, which is acontinuation-in-part of U.S. application Ser. No. 08/941,978, filed Oct.1, 1997, the entire contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an improved wire pull backdelivery system. More specifically, the invention relates to a wirepull-back stent delivery system which utilizes a shape memorycontraction member to retract the retractable outer sheath and deploy amedical implant for a minimally invasive application, such as anendovascular stent graft, vena cava filter, aneurysm repair particles,self-expanding stent, balloon expandable stent, or the like.

[0003] Delivery systems for deploying medical implants, such as anendovascular stent graft, vena cava filter, self-expanding stent,balloon expandable stent or the like, are a highly developed and wellknown field of medical technology. These medical devices have many wellknown uses and applications. In particular, a stent is a prosthesiswhich is generally tubular and which is expanded radially in a vessel orlumen to maintain its patency. Stents are widely used in body vessels,body canals, ducts or other body lumens. Balloon expandable stents aremounted on a balloon which when expanded delivers the stent, exertingradial force on the constricted portion of the body lumen tore-establish patency. A self-expanding stent is a stent which expandsfrom a compressed delivery position to its original diameter whenreleased from the delivery device, exerting radial force on theconstricted portion of the body lumen to re-establish patency. Onecommon self-expanding stent is manufactured of Nitinol, anickel-titanium shape memory alloy, which can be formed and annealed,deformed at a low temperature, and recalled to its original shape withheating, such as when deployed at body temperature in the body. A commonmaterial for balloon expandable stents is stainless steel.

[0004] Wire pull-back stent delivery systems commonly assigned with thisapplication include U.S. Pat. No. 5,571,135, U.S. Ser. No. 08/753,641filed Sep. 27, 1996 and U.S. Pat. No. 5,733,267, the entire contents ofwhich are hereby incorporated by reference. Another wire pull-back stentdelivery system is shown in U.S. Pat. No. 5,360,401. One importantfactor in delivering the stent is a controlled precise retraction of theretractable outer sheath. What is needed is a wire pull-back stentdelivery system which provides for a controlled and precise retractionof the retractable outer sheath and enables the physician to accuratelydetermine proper positioning of the stent.

SUMMARY OF THE INVENTION

[0005] The inventive stent delivery system includes a catheter having aretractable outer sheath near its distal end. A shape memory contractionmember having a memorized contracted shape is connected to theretractable outer sheath. A heat generating device connected to theshape memory contraction member causes the shape memory contractionmember to heat up to its transition temperature and assume itscontracted position, retracting the retractable outer sheath.

[0006] Another embodiment utilizes 2 springs, a “normal” spring and ashape memory alloy (SMA) spring, the two springs selected and designedso that the “normal” spring has an expansion force which is less thanSMA spring when the SMA spring is austenitic, but greater than the SMAspring when the SMA spring is martensitic.

[0007] Yet another embodiment utilizes a shape memory latch which in itsmartensitic state abuts a stop to prevent a spring from moving thesheath proximally, but in its austenitic state releases the stop,allowing the spring to retract the sheath to release the stent fordeployment.

BRIEF DESCRIPTION OF THE FIGURES

[0008]FIG. 1 shows a cross-sectional view of a first embodiment of theinventive catheter with a single coiled wire for its shape memorycontraction member;

[0009]FIG. 2 shows a cross-sectional view of a second embodiment of theinventive catheter with a balloon beneath the stent and with a coiland/or twisted wire contraction member;

[0010]FIG. 3 shows a cross-sectional view of a third embodiment of theinventive catheter with a multiple wire contraction member with thewires coiled in parallel;

[0011]FIG. 4 shows a cross-sectional view of a fourth embodiment of theinventive catheter with a braided wire tube contraction member;

[0012]FIG. 5 shows a schematic cross-sectional view of a fifthembodiment of a shape memory retraction catheter, shown in theundeployed position;

[0013]FIG. 6 shows a schematic cross-sectional view of a fifthembodiment of a shape memory retraction catheter, shown in the deployedposition;

[0014]FIG. 7 shows a schematic cross-sectional view of a sixthembodiment of a shape memory retraction catheter, showing in theundeployed position;

[0015]FIG. 8 shows a schematic cross-sectional view of a sixthembodiment of a shape memory retraction catheter, shown in the deployedposition;

[0016]FIG. 9 shows the shape memory latch of the sixth embodiment in itsmartensitic state, and

[0017]FIG. 10 shows the shape memory latch of the sixth embodiment inits austenitic state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring to FIG. 1, the inventive catheter is shown generally at10 and is of well known construction with an inner shaft 12 and an outershaft 14. Connected to the outer shaft 14 is a retraction assembly showngenerally at 16, which is comprised of a collapsible accordian section18 and a stent sheath section 20. For more information on thecollapsible retractable sheath please refer to U.S. Pat. No. 5,534,007and PCT/US96/07143 filed May 17, 1996, both of which are commonly ownedwith this application and the entire contents of which are herebyincorporated by reference.

[0019] A medical device such as stent 22 is carried on inner shaft 12under retraction assembly 16, as is well known in the art. Stent 22 canbe self-expanding or balloon expandable. The inventive catheter may beused to delivery endovascular stent grafts, vena cava filters, aneurysmrepair particles, self-expanding stents, balloon expandable stents, orthe like.

[0020] An annular collar 26 is attached to the proximal portion of stentsheath 20 and a shape memory contraction member 28 is connected toannular collar 26. In this embodiment the shape memory contractionmember 28 is a one-way Nitinol coiled wire spring, which aftermartensitic to austenitic transition has a shortened longitudinallength, causing annular collar 26 to be retracted proximally, collapsingaccordian section 18 of the retractable outer sheath 16 and retractingstent sheath 20 so the medical device such as stent 22 can be delivered.

[0021] As is well known in the art Nitinol can be made with anaustenitic final (A_(f)) temperature above body temperature. At roomtemperature the Nitinol wire is in its martensite phase and can beeasily deformed. In the first embodiment the contraction member 28 ismade from Nitinol wire, formed into a coil and heat set into a springshape. After the spring is made, the spring is deformed at roomtemperature to elongate the spring. One end of the spring is attached tothe annular collar 26 and the other end is fixedly attached to the innershaft 12, at bumper 37.

[0022] In the first embodiment the shape memory contraction member 28takes the form of a spring, however it should be understood that anygeometry which resulted in a reduced longitudinal length, causingretraction could be utilized. The length of the spring would determinethe amount of retraction and can be selected for various size stents. Analternate embodiment is an elongate Nitinol wire which shortens uplongitudinally upon transition (muscle wire). With a one meter long wirewhich contracts 8% for example, a retraction of 80 mm could be provided,which is adequate for the various stent lengths in common use. Othershape memory alloys can provide various longitudinal contraction as apercent of length and could be utilized as well, if desired. Contractionmember 28 could also take a zig-zag shape. The single wire 28 could alsobe replaced with a plurality of smaller diameter wires which could bebraided, intertwined or the like, discussed below in more detail inconnection with FIGS. 2 and 3.

[0023] Power supply 30 supplies power to rheostat 32 which suppliescurrent to the Nitinol spring 28 via lead wire 34. The Nitinol spring 28acts as a resistor and heats up, which causes the Nitinol to go throughits transition temperature and assume its memorized shape. Thetransition temperature must be above body temperature. When the currentflow is stopped, the spring 28 will stop contracting. Depending on themedium surrounding the spring 28 heat loss will vary and hence the timeto stop contraction will vary as well. By replacing a manually operatedpull wire with the inventive shape memory contraction member greatercontrol of the retraction is achieved by using the rheostat to controlthe electrical input into the system. This will eliminate the jerkingwhich can result from manual retraction of a pull wire, which can becaused by excessive force being used to overcome the high frictional andcompressive forces created with larger stents.

[0024] Positive lead wire 34 is connected to contraction member 28through contraction chamber 39. The negative lead wire is shown at 35.Contraction member 28 extends through contraction chamber 39 and isattached to annular collar 26. To protect the body from electrical andthermal conduction, either the contraction member 28 or contractionchamber 39 or both may be thermally and/or electrically insulated.

[0025] Although in the first embodiment the section of the contractionmember 28 between contraction chamber 39 and annular collar 26 isNitinol, contraction member 28 could be made of a different materialsuch as stainless steel if desired. The geometry of the spring coilprovides the contraction which retracts the outer sheath 16, so only theportions of contraction member 28 in the contraction chamber 39 needs tobe manufactured of shape memory alloy.

[0026] Referring now to FIG. 2, stent 22 is shown with balloon 24beneath it for dilation of a balloon expandable stent. Stent sheath 20acts as a protective sheath for the stent and is withdrawn using shapememory actuator 28. The actuator or contraction member 28 is shown asmultiple wires twisted and/or braided together.

[0027] Referring now to FIG. 3, a third preferred embodiment of theinventive catheter is shown in which actuator 28 is comprised ofmultiple wires coiled in parallel. If the wires are insulated, thedistal ends of the wires can be connected and the wire leads are thenboth at the proximal end of the contraction member 28. Using smallerwires coiled in parallel enables the profile of the actuator 28 to bereduced while maintaining the ability to generate the same retractionforce as a single larger wire. In this embodiment the accordian section18 is replaced with a sliding sleeve design where stent sheath 20 movesproximally over the contraction chamber lumen 40 during retraction ofstent sheath 20 to expose stent 22. The sliding sleeve section couldalso be designed to slid under lumen 40 if desired.

[0028] Referring now to FIG. 4, a fourth embodiment of the inventivecatheter is shown in which the contraction member 41 is a shape memorybraided wire tube. Shape memory contraction member 41 is connected tostent sheath 20 via annular collar 26. Upon heating, shape memorycontraction member 41, moves proximally, hence moving stent sheath 20proximally.

[0029] It should be understood from the above description of thedifferent embodiments that the contraction member may consist of singlewires, parallel wires, braided wires, twisted wires, or combinationsthereof shaped into a coil. Also, the contraction member could consistof a braided tube comprised of single wires, parallel wires, braidedwires, twisted wires, or combinations thereof.

[0030] It should also be understood that contraction member 28 or 41could be heated using current, as in FIGS. 1-4, or could be heatedconductively, either by being conductively connected to a heat source orby being bathed in a warm fluid bath.

[0031] It should also be understood that the shape memory contractionmember 28 or 41 could be manufactured of one-way or two-way shape memoryalloy. As is well known in the art two-way shape memory alloy takes twodifferent shapes with different temperatures. Therefore, with two-wayshape memory alloy contraction member 28 could contract at a firsttemperature selected during manufacture and expand at a second selectedtemperature. This would allow the retractable outer sheath 16 to beclosed if the user changed their mind about delivery or during delivery.

[0032] The inventive device can deliver other medical devices other thanstents and can be used in connection with fixed wire, single operatorexchange (SOE)/rapid exchange (RX) or over the wire (OTW) catheterconfigurations.

[0033] A fifth embodiment of a shape memory retraction catheter is shownin FIGS. 5 and 6, which shows a schematic view of a distal end of acatheter in both an undeployed and deployed position, shown respectivelyin FIGS. 5 and 6. In this embodiment a shape memory alloy retractiondevice is utilized to retract sheath 20 to release stent 22 fordeployment. The shape memory alloy retraction device consists of firstcompressed spring 50, which is fixedly attached to the distal end of thecatheter at 52 and is attached to the annular at 54, and second spring56 which is attached to the annular collar at 58 and fixedly attached tothe catheter at 60. Second compressed spring 56 is made of a shapememory alloy (SMA) which is formulated to be austenite at bodytemperature, which is approximately 37° C., and is designed to exert adistal force which is greater than the proximal force of first spring 50at body temperature. First spring 50 is not made of shape memory alloyin the preferred embodiment, but could be made of SMA with a very lowA_(f) temperature, so that it did not change states with the cold waterflush. Cold water flushing causes second spring 56 to transform to amartensite state, in which the proximal force exerted by spring 50,which is not affected by the cold water flushing, is greater than thedistal force of second spring 56. The greater force exerted by spring 50when spring 56 is martensitic moves the sheath 20 proximally to releasethe stent 22 for deployment. Although cold water flushing is preferred,it should be understood that any known medium cooling device could beutilized to cause second spring 50 to transform. With suitable designchanges and if desired, second spring 56 could be heat actuated, if thetransformation temperature is above body temperature.

[0034] An important feature of the fifth embodiment is that springs 50and 56 are designed so that spring 50 has a proximal force which is lessthan the distal force of second spring 56 when spring 56 is austenitic,but greater than the distal force of spring 56 when spring 56 ismartensitic. However, it should be understood that the positions offirst spring 50 and second spring 56 could be switched and by suitableand opposite selection and design, second spring 56 could exert aproximal force on the sheath 20 which is less than the distal forceexerted on the sheath 20 by the first spring 50, when the second spring56 is in its martensitic state. However, when spring 56 is in itsaustenitic state it could be selected and designed to exert a proximalforce on sheath 20 which is greater than the distal force exerted on thesheath 20 by the first spring 50.

[0035] An alternate embodiment for the device of FIGS. 5 and 6 would beto make both spring 50 and spring 56 of nitinol with equal A_(f)>37° C.(i.e. martensite at body temperature). With each of spring 50 and 56connected to its own separate electric resistance heating (not shown),sheath 20 could be cycled back and forth as alternate springs 50 and 56change from martensite to austenite by resistance heating.

[0036] A sixth embodiment of a shape memory retraction catheter is shownin FIGS. 7 and 8, which shows a schematic view of a distal end of acatheter in both an undeployed and deployed position, shown respectivelyin FIGS. 7 and 8. In this embodiment the retractable sheath 20 includesa stop 60 extending from the proximal end of sheath 20. Stop 60 isengaged by a shape memory latch 62, which is fixedly attached to thecatheter. A compressed spring 64 is arranged to exert a proximal forceon sheath 20, which is held in the undeployed state by shape memorylatch 62 as shown in FIG. 7. In FIG. 8, latch 62 is shown in a releasedposition, which allows spring 64 to move sheath 20 proximally to releasethe stent 22 for deployment. Latch 62 may be actuated by either coolingor heating as discussed above, with suitable material selection. Itshould also be understood that latch 62 could be designed to soften topermit retraction.

[0037] The shape memory latch 62 is shown in both its engaged andreleased states in FIGS. 9 and 10, respectively. As seen in FIG. 9, whenthe latch tip 66 is in its martensitic state, it angles downwardly toabut stop 60. As seen in FIG. 10, when the latch tip 66 is in itsaustenitic state, it straightens to release stop 60, allowing spring 64to move sheath 20 proximally.

[0038] The above Examples and disclosure are intended to be illustrativeand not exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

What is claimed is as follows:
 1. A catheter comprising: a catheter bodyhaving proximal and distal ends and including a retractable outer sheathnear the distal end of the catheter body; a shape memory retractiondevice having a first state above a predetermined temperature and asecond state below the predetermined temperature, the shape memoryretraction device operatively connected to the retractable outer sheathand being constructed and arranged so that in the first state theretractable outer sheath is in an undeployed state and in the secondstate the retractable outer sheath is in a deployed state.
 2. Thecatheter of claim 1 wherein the first state of the shape memoryretraction device is austenitic.
 3. The catheter of claim 1 wherein thefirst state of the shape memory retraction device is martensitic.
 4. Thecatheter of claim 2 wherein the shape memory retraction device comprisesa first “normal” spring portion connected to the retractable outersheath to provide a proximal retraction force, and a second shape memoryalloy spring portion connected to the retractable outer sheath toprovide a distal opposing force, the first and second spring portionsbeing selected and designed so that the proximal retraction force isless than the distal opposing force when the second shape memory alloyspring portion is in its austenitic state, but where the proximalretraction force is greater than the distal opposing force when thesecond shape memory alloy spring portion is in its martensitic state. 5.The catheter of claim 3 wherein the shape memory retraction devicecomprises a first “normal” spring portion connected to the retractableouter sheath to provide a distal opposing force, and a second shapememory alloy spring portion connected to the retractable outer sheath toprovide a proximal retraction force, the first and second springportions being selected and designed so that the proximal retractionforce is less than the distal opposing force when the second shapememory alloy spring portion is in its martensitic state, but where theproximal retraction force is greater than the distal opposing force whenthe second shape memory alloy spring portion is in its austenitic state.6. The catheter of claim 1 wherein the shape memory retraction device iscomprised of a spring connected to the retractable outer sheath toprovide a proximal retraction force and a second shape memory deviceconnected to the catheter body and having first and second states, thesecond shape memory device in its first state being operativelyconnected to the retractable outer sheath to prevent the retraction ofthe outer sheath, and in its second state releases the retractable outersheath so that the spring may retract the sheath to its deployed state.7. The catheter of claim 1 wherein the second shape memory device iscomprised of a latch connected to the catheter body, the shape memorylatch in its first state being operatively connected to the retractableouter sheath to prevent the retraction of the outer sheath, and in itssecond state releases the retractable outer sheath so that the springmay retract the sheath to its deployed state.
 8. The catheter of claim 7wherein the first state of the shape memory latch is martensitic.
 9. Thecatheter of claim 8 wherein the retractable outer sheath includes a stopwhich extends proximally to abut the shape memory latch when it is inits martensitic state.
 10. The catheter of claim 7 wherein the shapememory latch is softened in its second state to release the retractableouter sheath.